Responses of Primates to Landscape Change in Amazonian Land‐bridge islands—a Multi‐scale Analysis

Large hydroelectric dams are one of the current drivers of habitat loss across Amazonian forests. We investigated how the primate community at a hydroelectric dam in Brazilian Amazonia responded to changes in the landscape and local habitat structure of land‐bridge islands after 21 yr of post‐isolation history. The Balbina Dam, constructed in 1986, inundated 3129 km² of primary forests and created more than 3500 variable‐sized islands. We conducted primate and habitat structure surveys on 20 islands from 5 to 1815 ha, and extracted forest patch and landscape metrics for each island. The number of primate species per island varied between 0 and 7 species. Primate composition varied substantially according to both island area and forest cover remaining within the landscape, whereas island area alone was the most significant predictor of richness. Locally, tree density and vertical stratification were the most significant explanatory variables of primate composition and richness. A model containing area effects had the most explanatory power regarding site occupancy for most species. Individually, each species responded differently, with howler and brown capuchin monkeys showing greater tolerance to cope with habitat changes. Body size was also an important predictor of primate occupancy. We recommend protecting large fragments and enhancing the suitability of surrounding habitats to ensure primate conservation in most Neotropical fragmented landscapes. Given the flat topography of hydroelectric reservoirs, which mainly favors the formation of small islands, and the escalating hydropower development plans in Amazonia, our findings provide evidence for pervasive detrimental impacts of dams on primate communities.     

片段化景观中壳斗科植物种子捕食和扩散模式

生境片段化伴随的面积效应和边缘效应, 可改变分散贮食动物的竞争强度、觅食行为以及隐蔽条件, 影响种子捕食和扩散模式。阐明生境片段化对多物种种子捕食和扩散的影响, 对理解片段化生境中的植物更新和生物多样性维持十分重要。该研究在浙江省千岛湖地区的岛屿和大陆上开展了针对6种壳斗科植物的种子捕食和扩散实验, 分析了物种、分散贮食动物相对多度、种子产量、岛屿大小和边缘效应如何共同影响种子命运和种子扩散距离。主要结果: (1)种子命运和扩散距离在物种间存在显著差异; (2)大陆比岛屿有更长的种子留存时间, 小岛种子留存时间最短, 岛屿内部比岛屿边缘有更长的种子留存时间; (3)物种和岛屿大小对种子原地取食率存在交互作用, 白栎(Quercus fabri)种子在大岛上有更高的原地取食率; (4)种子在小岛上有最高的扩散率, 分散贮食动物相对多度对种子扩散后贮藏率有负效应。表明在千岛湖地区, 生境片段化改变了种子捕食和扩散模式, 且面积效应对不同物种的种子捕食和扩散模式产生了不同作用, 从而影响森林群落更新和生物多样性维持。     

Assemblage-level responses of phyllostomid bats to tropical forest fragmentation: land-bridge islands as a model system

Aim Working within a system of high structural contrast between fragments and the surrounding matrix, we assessed patterns of species loss and changes in species composition of phyllostomid bats on artificial land‐bridge islands relative to mainland assemblages, and evaluated the responses of bats to forest edges. We further examined the relative influence of local‐scale characteristics (e.g. vegetation structure, island area) versus landscape attributes (e.g. forest cover, patch density) and the importance of spatial scale in determining phyllostomid species richness and composition on islands. Location Islands in Gatún Lake and adjacent mainland peninsulas in the Barro Colorado Nature Monument, Panama. Methods Bats were sampled over a 2‐year period on 11 islands as well as at forest‐edge and interior sites on adjacent mainland, resulting in > 8400 captures. Results The islands harboured a less diverse and structurally simplified phyllostomid bat fauna. Islands far from the mainland were especially species‐poor. This decline in species richness was associated with compositional shifts towards assemblages strongly dominated by frugivores with good dispersal abilities. Members of other ensembles, most importantly gleaning animalivores, were much less common or absent. Although overall species composition was not significantly altered, species richness at continuous forest‐edge sites was significantly lower compared with that at interior sites. Distance from the mainland and amount of forest cover in the landscape were the best predictors of species richness and assemblage composition. Responses were scale‐dependent. At the local scale, species richness was independent of island area but was correlated positively with distance from the mainland. In contrast, area effects became more important at larger spatial scales, suggesting that many species use multiple fragments. Main conclusions Our results underline the conservation value of small habitat remnants, which, even when embedded in a hostile matrix, can support a relatively diverse bat fauna, provided that there is a low degree of patch isolation and spatial proximity to larger tracts of continuous forest. Although the results at the assemblage level were inconclusive, we demonstrate that certain bat species and ensembles, particularly gleaning animalivores, exhibit high edge‐sensitivity. Our results point to habitat loss rather than changes in landscape configuration as the main process after isolation underlying phyllostomid bat responses, suggesting that conservation efforts should focus on habitat preservation instead of trying to minimize fragmentation per se at the expense of habitat amount.     

Abundance-age-area relationships in an insular plant community

Two processes are thought to generate positive relationships between species richness and island area. The areaper se hypothesis states that larger islands maintain larger populations, which are less susceptible to extinction. The habitat hypothesis states that larger islands contain more habitats, and therefore a greater number of habitat specialists. However, the importance of each mechanism is debated. I tested the areaper se and habitat hypotheses by comparing relationships between plant abundance, age and island area in five shrub species on islands off the coast of British Columbia, Canada. Results showed that two shrub species increased in both abundance and age with island area. The remaining three species showed no differences in abundance and age with island area. Conifer abundances increased with island area, which generated differences in habitat availability. Smaller islands were dominated by open habitat, while larger islands contained both open and forested habitats. Changes in habitat availability with island area could explain patterns in plant abundance and age. The two species that increased in abundance with island area were commonly found in conifer forest on the mainland, and their distributions were consistent with the distribution forest habitat. Positive relationships between plant age and island area in these two species may result from lower survivorship in the open habitat, which dominated small islands. The three species that showed no relationship between abundance and island area are commonly found in open habitat on the mainland, and their island distributions paralleled the availability of open habitat on islands. Similar plant ages on different sized islands may result from their occurrence in open habitat on both large and small islands. Overall results support the habitat hypothesis and indicate that species distributions result from the interaction between habitat affinities and changes in habitat availability with island area.     

Island theory, matrix effects and species richness patterns in habitat fragments

Island biogeography theory, created initially to study diversity patterns on islands, is often applied to habitat fragments. A key but largely untested assumption of this application of theory is that landscape matrix species composition is non‐overlapping with that of the islands. We tested this assumption in successional old field patches in a closely mowed matrix, and because our patches are appropriately viewed as sets of contiguous habitat units we studied patterns of species richness per unit area. Previous studies at our site did not find that diversity patterns on patch ‘islands’ conformed to predictions of island biogeography theory. Our results indicate that when matrix species are removed from the patch samples, diversity patterns conform better to theory. We suggest that classical island theory remains an appropriate tool to study diversity patterns in fragmented habitats, but that allowances should be made for spill‐over colonization of ‘islands’ from the ‘sea’.     

Long‐term colonization ecology of forest‐dwelling species in a fragmented rural landscape – dispersal versus establishment

Species colonization in a new habitat patch is an efficiency indicator of biodiversity conservation. Colonization is a two‐step process of dispersal and establishment, characterized by the compatibility of plant traits with landscape structure and habitat conditions. Therefore, ecological trait profiling of specialist species is initially required to estimate the relative importance of colonization filters. Old planted parks best satisfy the criteria of a newly created and structurally matured habitat for forest‐dwelling plant species. We sampled species in 230 ancient deciduous forests (source habitat), 74 closed‐canopy manor parks (target habitats), 151 linear wooded habitats (landscape corridors), and 97 open habitats (isolating matrix) in Estonia. We defined two species groups of interest: forest (107 species) and corridor specialists (53 species). An extra group of open habitat specialists was extracted for trait scaling. Differing from expectations, forest specialists have high plasticity in reproduction mechanisms: smaller seeds, larger dispersules, complementary selfing ability, and diversity of dispersal vectors. Forest specialists are shorter, less nutrient‐demanding and mycorrhizal‐dependent, stress‐tolerant disturbance‐sensitive competitors, while corridor specialists are large‐seeded disturbance‐tolerant competitors. About 40% of species from local species pools have immigrated into parks. The historic forest area, establishment‐related traits, and stand quality enhance the colonization of forest specialists. The openness of landscape and mowing in the park facilitate corridor specialists. Species traits in parks vary between a forest and corridor specialist, except for earlier flowering and larger propagules. Forest species are not dispersal limited, but they continue to be limited by habitat properties even in the long term. Therefore, the shady parts of historic parks should be appreciated as important forest biodiversity‐enhancing landscape structures. The habitat quality of secondary stands can be improved by nurturing a heterogeneous shrub and tree layer, and modest herb layer management.     

Winter bird communities in the Åland archipelago: an island biogeographic point of view

The distribution of wintering land birds was examined in the archipelago of Åland (60°N, 20°E) along two ecological dimensions: (1) the island continuum from small skerries ((0.5 ha) to the mainland of Åland (97000 ha), and (2) the habitat range of the mainland of Åland. In the species-area relationship, both the exponential and power function models fitted well. The increase of the number of species with island size was interpreted as a consequence of increasing habitat diversity on larger islands. The smallest islands supported only few seed-eating species utilizing the islands in a fine-grained fashion; none of these birds belonged to the breeding fauna of the islands. With increasing island size and habitat diversity, insectivores and species tied to the human culture were added. On the mainland of Åland, more than half of the birds were observed near human habitations: bird communities wintering in pine forests were richer than in deciduous forests. Proportion of wintering species was greatest in the breeding communities of pine forests. The proportion of wintering species was presumably regulated by the degree of structural change in the habitat between summer and winter, this change being most drastic in deciduous habitats The species observed could be broadly classified into three feeding categories: opportunists ., omnivores and scavengers, dependent on the diverse food items provided by man; food specialists , species éating seeds and berries, ranging widely in the islands and habitats; and insectivorous habitat specialists , inhabiting coniferous habitats, and islands with coniferous (pine) forests. Opportunists, in particular, gel increasing wintering opportunities by the impact of man.     

Factors determining mammal species richness on habitat islands and isolates: habitat diversity, disturbance, species interactions and guild assembly rules

• 1 For over three decades the equilibrium theory of island biogeography has galvanized studies in ecological biogeography. Studies of oceanic islands and of natural habitat islands share some similarities to continental studies, particularly in developed regions where habitat fragmentation results from many land uses. Increasingly, remnant habitat is in the form of isolates created by the clearing and destruction of natural areas. Future evolution of a theory to predict patterns of species abundance may well come from the application of island biogeography to habitat fragments or isolates.
• 2 In this paper we consider four factors other than area and isolation that influence the number and type of mammal species coexisting in one place: habitat diversity, habitat disturbance, species interactions and guild assembly rules. In all examples our data derive from mainland habitat, fragmented to differing degrees, with different levels of isolation.
• 3 Habitat diversity is seen to be a good predictor of species richness. Increased levels of disturbance produce a relatively greater decrease in species richness on smaller than on larger isolates. Species interactions in the recolonization of highly disturbed sites, such as regenerating mined sites, is analogous to island colonization. Species replacement sequences in secondary successions indicate not just how many, but which species are included. Lastly, the complement of species established on islands, or in insular habitats, may be governed by guild assembly rules. These contributions may assist in taking a renewed theory into the new millennium.

     

Bat species richness and abundance in tropical rain forest fragments and in agricultural habitats at Los Tuxtlas, Mexico

Faced with the rapid and extensive conversion of tropical rain forests to pasture lands and agricultural fields and with the need to preserve the remaining mammalian fauna, it is imperative to determine how the different species that form the mammalian community have responded to the anthropogenic alterations of their natural habitats To provide data in this direction, we sampled bats m 45 forest islands, m 20 agricultural habitats representing five types of vegetation (cocoa, coffee, mixed, citrus and allspice), in four live-fence sites and in four pasture sites at Los Tuxtlas, Veracruz, Mexico Sampling effort resulted in the capture of 2587 bats representing 35 species In forest habitats we detected 32 species We did not capture any bats at the four pasture sites, but the at the other agricultural habitats studied, we captured 38% of the bats and 77% of the species recorded Thirty-four percent of the species recorded were present at the live-fence habitats Isolating distance was an important variable influencing species richness in forests and in agricultural habitats Only 10% of the species recorded occurred m all the habitats studied, but 77% of the species occurred m a habitat other than ram forest Recaptures of bats indicated inter habitat movements in the fragmented landscape We discuss the conservation value for the bat fauna of agricultural islands of vegetation as elements reducing isolating distances among forest fragments     

Forest Loss and the Biodiversity Threshold: An Evaluation Considering Species Habitat Requirements and the Use of Matrix Habitats

Habitat loss is the main driver of the current biodiversity crisis, a landscape-scale process that affects the survival of spatially-structured populations. Although it is well-established that species responses to habitat loss can be abrupt, the existence of a biodiversity threshold is still the cause of much controversy in the literature and would require that most species respond similarly to the loss of native vegetation. Here we test the existence of a biodiversity threshold, i.e. an abrupt decline in species richness, with habitat loss. We draw on a spatially-replicated dataset on Atlantic forest small mammals, consisting of 16 sampling sites divided between forests and matrix habitats in each of five 3600-ha landscapes (varying from 5% to 45% forest cover), and on an a priori classification of species into habitat requirement categories (forest specialists, habitat generalists and open-area specialists). Forest specialists declined abruptly below 30% of forest cover, and spillover to the matrix occurred only in more forested landscapes. Generalists responded positively to landscape heterogeneity, peaking at intermediary levels of forest cover. Open area specialists dominated the matrix and did not spillover to forests. As a result of these distinct responses, we observed a biodiversity threshold for the small mammal community below 30% forest cover, and a peak in species richness just above this threshold. Our results highlight that cross habitat spillover may be asymmetrical and contingent on landscape context, occurring mainly from forests to the matrix and only in more forested landscapes. Moreover, they indicate the potential for biodiversity thresholds in human-modified landscapes, and the importance of landscape heterogeneity to biodiversity. Since forest loss affected not only the conservation value of forest patches, but also the potential for biodiversity-mediated services in anthropogenic habitats, our work indicates the importance of proactive measures to avoid human-modified landscapes to cross this threshold.     

Island biogeography of temporary wetland carabid beetle communities

Aim The study tests if island biogeography is applicable to invertebrate communities of habitat islands in the agricultural landscape that are not fragments of formerly larger habitats. Location Thirty temporary wetlands in the agricultural landscape of northeast Germany. Methods The composition and species richness of carabid beetle communities was analysed. Habitat area, isolation, the density of temporary wetlands in the landscape, land‐use intensity and the maximum duration of flooding were recorded as independent variables. Overall species richness and wetland species richness were studied in independent regression analyses. The community composition was analysed by means of a Canonical Correspondence Analysis (CCA). A partial CCA was used to analyse the effect of the distance to the edge of the field after removing impacts of other independent variables. Results The area of the habitats and various measures of isolation (mean distances = 81–240 m) did not influence species richness or wetland species richness. The community composition was mainly determined by the land‐use intensity, habitat area did not have significant effects, and the distance to the edge of the field was the only effective isolation parameter. Short‐winged species were more often affected by the distance to the edge of the field than full‐winged species. Main conclusion There is evidence that the distances between the wetlands do not provide an effective barrier to the species dispersal and, therefore, metapopulation structures including subpopulations of multiple temporary wetlands might counteract local area effects on subpopulations. Short‐winged species, however, might be more affected by isolation than full‐winged species. As carabid beetle community structure in most early successional habitats is similar, these results may be representative of many agricultural landscape habitats. Nature conservancy concepts that aim to increase habitat area and habitat connectivity have successfully been applied to fragmented late‐successional habitats. The present study indicates that such concepts do not necessarily result in higher diversity or larger populations in early successional habitats.     

Island biogeography extends to small-scale habitats: low competitor density and richness on islands may drive trait variation in nonnative plants

Previous island biogeography studies have quantified species richness on the scale of entire islands rather than smaller scales relevant to plant-to-plant competitive interactions. Further, they have not accounted for density compensation. Using mainland and island sites along the New England coast, we asked two questions. First, are both richness and density lower in small-scale habitats within islands than in similar mainland habitats? Second, do differences in competitor richness and density drive post-establishment trait variation in nonnative plant species? We used field surveys and individual-based rarefaction to estimate richness and density in 100-m² plots and demonstrated that island sites have significantly fewer species and individuals per unit area than mainland sites. We then conducted a field study in which we removed competing neighbors from nonnative plant individuals and found that when competitors were removed, individuals in low-competition environments demonstrated a lesser increase in vegetative growth but a greater increase in reproductive effort and herbivore tolerance relative to mainland individuals whose neighbors were also removed. We found that the central concept of island biogeography, i.e., that islands host fewer species than comparable mainland habitats, can be extended to smaller-scale habitats and that this difference in competitive pressure between mainland and island habitats can act as a driver of trait variation in nonnative plants.     

The influence of matrix and edges on species richness patterns of ground beetles (Coleoptera: Carabidae) in habitat islands

Aim The aim of this study was to analyse whether, and how, the inclusion of habitat specialists and edge‐preferring species modifies the species–area relationship predictions of the island biogeography theory for an insect group (ground beetles, Coloptera: Carabidae) living in natural fragments. Species–habitat island area relationships applied to terrestrial habitat islands can be distorted by the indiscriminate inclusion of all species occurring in the fragments. Matrices surrounding terrestrial habitat fragments can provide colonists that do not necessarily distinguish the fragment from the matrix and can survive and reproduce there. Edge‐preferring species can further distort the expected relationship, as smaller fragments have larger edge:core ratios. Location Nineteen forest fragments were studied in the Bereg Plain, Hungary, and SW Ukraine. This area contains natural forest patches, mainly of oak and hornbeam, and supports a mountain entomofauna. Methods Ground beetles (Carabidae) present in the 19 forest patches were categorized into generalists, forest specialists and edge‐preferring species. We analysed the relationship between species richness and fragment area using species richness in the different categories. Results The assemblages contained a high share of generalist species (species that occur also in the surrounding matrix). Forest patch size and the number of generalist species showed a marginally significant negative relationship, indicating that generalist species were more important in smaller patches. Forest specialist species richness was correlated positively with patch area. Edge‐preferring species were shown to influence the species–area relationship: the number of edge‐preferring species increased with the edge:area ratio. Main conclusions Both generalist and edge‐preferring species can considerably distort the species–area relationship. Island biogeography theory can be applied to habitat islands only if the habitat islands are defined correctly from the viewpoint of the target species.     

Butterfly diversity in Mediterranean islands and in Pentadaktylos <Emphasis Type="Italic">Pinus</Emphasis><Emphasis Type="BoldItalic"> </Emphasis><Emphasis Type="Italic">brutia</Emphasis> forests of Cyprus

We analysed the influence of contemporary geography on butterfly diversity for islands in the Mediterranean Basin. We found that island size and distance from the mainland has a significant effect on the number of species. We also used butterflies as an indicator group to identify the importance of forest habitats for biodiversity conservation in the island of Cyprus. To understand the relative importance of local vegetation characteristics of butterflies in the Pentadaktylos mountains transect counts were used to assess the abundance and butterfly diversity in two different forest types. A total of 1,602 butterflies and 23 species were recorded during this research. We observed highly significant effects of forest type on abundance and species richness of butterflies. For example, number of butterflies was significantly higher in old forest than young pine forest. Also, the abundance of endemic butterflies was highest in old forest habitats. Therefore, the survival of the majority of endemic butterflies in Cyprus may depend on conservation of old forests and their understorey plants.     

60 years of the equilibrium theory of insular biogeography: problems of testing, results of the field studies, applied importance

A review is presented of publications dealing with analysis of species richness of island biological communities and habitat islands based on the equilibrium theory of insular biogeography by MacArthur and Wilson (1963). Principal points of the theory are considered along with its shortcomings, problems and results of its testing. Also, possibilities are appraised for using recommendations elaborated on the base of the theory in nature conservation practice. The results of island and habitat island biota studies indicate that in many cases data corroborate the equilibrium theory while in many other cases they do not. In particular, for cenoses fragmented 50-250 years ago, especially for the ones formed by long living species, there have been no conspicuous effects of species relaxation detected. At that, the theory prediction of substantial reduction in species richness of fragmented communities in the long run is hardly disputed. The results of studies conducted in the field of insular biogeography are taken as a basis for recommendations on the long-term conservation of isolated communities integrity, although mostly they are of qualitative nature.     

Do forest-dwelling plant species disperse along landscape corridors?

Woody corridors in fragmented landscapes have been proposed as alternative habitats for forest plants, but the great variation in species-specific responses blurs the overall assessment. The aim of this study was to estimate the dispersal success of forest-dwelling plants from a stand into and along an attached woody corridor, and to explain the observed patterns from the point of view of species’ dispersal traits and corridor properties. We sampled 47 forest–corridor transects in the agricultural landscapes of southeastern Estonia. Regionally common forest-dwelling species (observed in at least 10 % of seed-source forests) were classified on the basis of their ecological response profile—forest-restricted species (F-type) and forest-dwelling generalists (G-type). Species richness and the proportion of F-type species decreased sharply from the seed-source forest core to the forest edge and to the first 10–15 m of the corridor, while G-type species richness remained constant throughout the transect. Corridor structure had a species-specific effect—F species were promoted by old (≥50 years) and wide (≥10 m) corridors, while G species were supported by young and narrow corridors with ditch-related soil disturbances. Moderate shade (canopy cover <75 %) was optimal for all forest-dwelling species. Large dispersule weight, and not seed weight, dispersal vector or Ellenberg’s indicator values, was the trait that differentiated F species from G species. We conclude that most woody corridors are only dispersal stepping-stone habitats for habitat generalist species, and not for specialists. Only century old corridors can relieve the dispersal limitation of forest-restricted species.     

Roles of fragmented and logged forests for bird communities in industrial Acacia mangium plantations in Indonesia

Industrial timber plantations severely impact biodiversity in Southeast Asia. Forest fragments survive within plantations, but their conservation value in highly deforested landscapes in Southeast Asia is poorly understood. In this study, we compared bird assemblages in acacia plantations and fragmented forests in South Sumatra to evaluate each habitat’s potential conservation value. To clarify the impact of habitat change, we also analyzed the response of feeding guild composition. Five habitat types were studied: large logged forest (LLF), burnt logged forest (BLF), remnant logged forest (RLF), 4-year-old acacia plantation (AP4), and 1-year-old acacia plantation (AP1). Estimated species richness (Chao 2) was highest in LLF then AP4 and BLF, while AP1 and RLF had lower estimated species richness. Community composition was roughly divided into two groups by non-metric multidimensional scaling ordination: acacia plantation and logged forest. Sallying substrate-gleaning insectivores, such as drongos, broadbills, and some flycatchers, were restricted to LLF, whereas acacia plantation hosted many terrestrial frugivores, such as doves. Although fragmented forests in our study site lacked several common tropical forest species, these fragments provide an important habitat for some sallying and terrestrial insectivores. A network of small riparian remnant forests could be a complementary habitat for some species, while the conservation value of burnt forest might be low. In conclusion, the highly fragmented forests in plantations are suboptimal habitats for birds but are still very important, because large primary forest blocks have been nearly lost in the surrounding landscape.     

Direct and indirect effects of area,energy and habitat heterogeneity on breeding bird communities

Aim To compare the ability of island biogeography theory, niche theory and species–energy theory to explain patterns of species richness and density for breeding bird communities across islands with contrasting characteristics. Location Thirty forested islands in two freshwater lakes in the boreal forest zone of northern Sweden (65°55′ N to 66°09′ N; 17°43′ E to 17°55′ E). Methods We performed bird censuses on 30 lake islands that have each previously been well characterized in terms of size, isolation, habitat heterogeneity (plant diversity and forest age), net primary productivity (NPP), and invertebrate prey abundance. To test the relative abilities of island biogeography theory, niche theory and species–energy theory to describe bird community patterns, we used both traditional statistical approaches (linear and multiple regressions) and structural equation modelling (SEM; in which both direct and indirect influences can be quantified). Results Using regression‐based approaches, area and bird abundance were the two most important predictors of bird species richness. However, when the data were analysed by SEM, area was not found to exert a direct effect on bird species richness. Instead, terrestrial prey abundance was the strongest predictor of bird abundance, and bird abundance in combination with NPP was the best predictor of bird species richness. Area was only of indirect importance through its positive effect on terrestrial prey abundance, but habitat heterogeneity and spatial subsidies (emerging aquatic insects) also showed important indirect influences. Thus, our results provided the strongest support for species–energy theory. Main conclusions Our results suggest that, by using statistical approaches that allow for analyses of both direct and indirect influences, a seemingly direct influence of area on species richness can be explained by greater energy availability on larger islands. As such, animal community patterns that seem to be in line with island biogeography theory may be primarily driven by energy availability. Our results also point to the need to consider several aspects of habitat quality (e.g. heterogeneity, NPP, prey availability and spatial subsidies) for successful management of breeding bird diversity at local spatial scales and in fragmented or insular habitats.     

Bird assemblages on Amazonian river islands: Patterns of species diversity and composition

The principles of island biogeography are rarely applied to the animal assemblages of Amazonian river islands. Here, we compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages were characterized by lower species richness and a higher abundance of a few dominant species. Additionally, the species composition of the islands was distinct from that of the mainland, including the nearby floodplain habitats. The number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbor an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial communities could be disproportionately threatened by river channel disturbances related to climate change or hydroelectric dam development. Abstract in Portughese is available with online material.     

Forest edges have high conservation value for bird communities in mosaic landscapes

A major conservation challenge in mosaic landscapes is to understand how trait‐specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi‐regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest‐edge‐open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait‐ and species‐specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long‐distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open‐habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape‐scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in longstanding fragmented landscapes.